Baluk, P. et al. Functionally specialized junctions between endothelial cells of lymphatic vessels. J. Exp. Med. 204, 2349-2362

Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143, USA.
Journal of Experimental Medicine (Impact Factor: 13.91). 11/2007; 204(10):2349-62. DOI: 10.1084/jem.20062596
Source: PubMed

ABSTRACT Recirculation of fluid and cells through lymphatic vessels plays a key role in normal tissue homeostasis, inflammatory diseases, and cancer. Despite recent advances in understanding lymphatic function (Alitalo, K., T. Tammela, and T.V. Petrova. 2005. Nature. 438:946-953), the cellular features responsible for entry of fluid and cells into lymphatics are incompletely understood. We report the presence of novel junctions between endothelial cells of initial lymphatics at likely sites of fluid entry. Overlapping flaps at borders of oak leaf-shaped endothelial cells of initial lymphatics lacked junctions at the tip but were anchored on the sides by discontinuous button-like junctions (buttons) that differed from conventional, continuous, zipper-like junctions (zippers) in collecting lymphatics and blood vessels. However, both buttons and zippers were composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, including occludin, claudin-5, zonula occludens-1, junctional adhesion molecule-A, and endothelial cell-selective adhesion molecule. In C57BL/6 mice, VE-cadherin was required for maintenance of junctional integrity, but platelet/endothelial cell adhesion molecule-1 was not. Growing tips of lymphatic sprouts had zippers, not buttons, suggesting that buttons are specialized junctions rather than immature ones. Our findings suggest that fluid enters throughout initial lymphatics via openings between buttons, which open and close without disrupting junctional integrity, but most leukocytes enter the proximal half of initial lymphatics.

  • Source
    • "To understand whether ANG2 regulates this transformation process, we treated pregnant females with the ANG2- blocking antibody starting from E12.5, before the transformation occurs, and analyzed the embryos at E18.5. At the sprouting vessel front, junctions in the IgG-treated lymphatics were zippers (Fig. 2A,B), consistent with the junctional pattern at the sprouting front reported elsewhere (Baluk et al. 2007; Yao et al. 2012), and ANG2 blockade did not affect this pattern (Fig. 2C,D). In the IgGtreated initial lymphatics behind the sprouts, the LEC shape was less elongated, and the junctions were clearly button-like (Fig. 2E,F). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Primitive lymphatic vessels are remodeled into functionally specialized initial and collecting lymphatics during development. Lymphatic endothelial cell (LEC) junctions in initial lymphatics transform from a zipper-like to a button-like pattern during collecting vessel development, but what regulates this process is largely unknown. Angiopoietin 2 (Ang2) deficiency leads to abnormal lymphatic vessels. Here we found that an ANG2-blocking antibody inhibited embryonic lymphangiogenesis, whereas endothelium-specific ANG2 overexpression induced lymphatic hyperplasia. ANG2 inhibition blocked VE-cadherin phosphorylation at tyrosine residue 685 and the concomitant formation of button-like junctions in initial lymphatics. The defective junctions were associated with impaired lymph uptake. In collecting lymphatics, adherens junctions were disrupted, and the vessels leaked upon ANG2 blockade or gene deletion. ANG2 inhibition also suppressed the onset of lymphatic valve formation and subsequent valve maturation. These data identify ANG2 as the first essential regulator of the functionally important interendothelial cell-cell junctions that form during lymphatic development.
    Genes & Development 07/2014; 28(14):1592-603. DOI:10.1101/gad.237677.114 · 12.64 Impact Factor
  • Source
    • "Lymphatic capillaries are ∼50 ␮m in diameter and do not have a basement membrane , continuous interendothelial junctions, pericytes, or smooth muscle cells. Instead, they consist of a single layer of endothelial cells that overlap slightly with " buttonlike " junctional protein expression, creating pores up to 2 ␮m in size allowing the one-way absorption of cells, fluid, and proteins [22]. The protein concentration of lymph is lower than blood [23] and the lymph flow rate is slow compared to the hepatic portal vein blood, so proteins that initially entered intestinal lymph may be less diluted than in blood. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Food proteins were considered to be absorbed into the body after being digested into amino acids, dipeptides and tripeptides. However, there were studies indicating that some proteins can pass through the intestinal epithelium under normal physiological conditions, perhaps not in sufficient quantities to be of nutritional importance, but in quantities that may be antigenically or biologically active. In the present study, rat intestinal lymph samples were collected using a modified lymph fistula rat model in fasted and cow's milk postprandial states. Low molecular weight proteins were enriched by ultrafiltration and differential solubilization, separated by 1D-SDS PAGE, digested in-gel based on molecular weight and identified using nanoLC-MS/MS. In the postprandial rat intestinal lymph, nine bovine-specific proteins (FDR≤1%) were identified in different molecular weight regions. Most proteins identified in lymph were highly abundant proteins in the milk, such as β-lactoglobulin and caseins. Seven of the nine identified bovine-specific proteins are allergens in milk. This strategy can be used to search for proteins that can enter the intestinal lymph and analyze their common features. Understanding the common features of these proteins might help to develop protein drugs taken orally, so that therapeutic proteins might embody fusion-domains for cross-barrier transport or translocation. This article is protected by copyright. All rights reserved.
    Proteomics 09/2013; 13(17). DOI:10.1002/pmic.201300097 · 3.97 Impact Factor
  • Source
    • "The ability of NPs to enter cells and pass through intercellular junctions also depends upon the size of the particulate. The endothelial lining of lymphatic capillaries has been described as discontinuous (Baluk et al. 2007), which may explain the ease with which the intercellular barriers of the lymphatics can be penetrated and the ability of phagocytic cells and large molecules to enter the lymphatic circulation. Importantly, lymphatic circulation is very important in systemic redistribution of particulates (Harmsen et al. 1987, 1985; Porter et al. 2010; Riviere 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Nanotechnology involves technology, science, and engineering in dimensions less than 100 nm. A virtually infinite number of potential nanoscale products can be produced from many different molecules and their combinations. The exponentially increasing number of nanoscale products will solve critical needs in engineering, science, and medicine. However, the virtually infinite number of potential nanotechnology products is a challenge for toxicologic pathologists. Because of their size, nanoparticulates can have therapeutic and toxic effects distinct from micron-sized particulates of the same composition. In the nanoscale, distinct intercellular and intracellular translocation pathways may provide a different distribution than that obtained by micron-sized particulates. Nanoparticulates interact with subcellular structures including microtubules, actin filaments, centrosomes, and chromatin; interactions that may be facilitated in the nanoscale. Features that distinguish nanoparticulates from fine particulates include increased surface area per unit mass and quantum effects. In addition, some nanotechnology products, including the fullerenes, have a novel and reactive surface. Augmented microscopic procedures including enhanced dark-field imaging, immunofluorescence, field-emission scanning electron microscopy, transmission electron microscopy, and confocal microscopy are useful when evaluating nanoparticulate toxicologic pathology. Thus, the pathology assessment is facilitated by understanding the unique features at the nanoscale and the tools that can assist in evaluating nanotoxicology studies.
    Toxicologic Pathology 02/2013; DOI:10.1177/0192623312467403 · 1.92 Impact Factor
Show more